This application in general relates to a unique system for injecting pressurized gas or fluid into a mold cavity in a plastic injection molding system.
Various methods are known to inject gas into a plastic injection molding system to form hollow portions within a part. Typically, gas is injected through an injection pin extending through an opening in the mold. The prior art injection pin sometimes extended through a separate gas aperture, which required another opening in the mold. This complicated the structure of the mold. One alternative in the prior art was to inject the gas through the plastic injection opening, or sprue. This complicated both the structure of the plastic injection opening and the flow of plastic into the system. Further, such structure often resulted in the injection pin gas passages becoming clogged. It would be desirable to reduce the number of openings in the mold body to reduce the complexity of the mold, and further to result in a smoother surface for the parts formed within the mold.
Prior art injection pins typically have a small gas passage leading into the mold. Molten plastic may enter and clog this passage. The gas passage may have a check valve disposed in it to prevent back flow. This complicates the structure of the injection pin and does not prevent plastic from entering and clogging the tip of the gas passage.
It is known to mount a movable injection pin within a mold that moves from a retracted position outside of the mold cavity, to an extended position within the cavity to inject the pressurized gas. With such systems, the injection pin typically moves through a separate aperture in the mold, thus requiring an additional mold opening. Further, such injection pins typically have a gas outlet at an axial end of the pin which faces the mold cavity. The fluent plastic entering the cavity may clog this open end of the injection pin.